Half of all pregnancies in the U.S. are unintended. Of these, half occur to women who were practicing contraception in the month they conceived, and others occur when couples stop use because they find their method difficult or inconvenient to use. Data from NSFG is used to compute life-table probabilities of contraceptive failure for reversible methods of contraception, discontinuation of use for a method-related reason and resumption of contraceptive use. Data indicate that within one year of starting to use a reversible method of contraception, 9% of women experience contraceptive failure 7% of those using pill, 9% male condom and 19% withdraw. During a lifetime of use of reversible methods, a typical woman will experience 1.8 contraceptive failures. Overall, 31% of women discontinue use of a reversible contraceptive for a method-related reason within six months of starting use and 44% do so within 12 months. However, 68% resume use within one month and 76% within 3 months. Using multivariate analyses the authors find that contraceptive failure is elevated among low-income women and Hispanic women. Low-income women are also less likely to resume use after discontinuation.